Electronic and information communication industries are rapidly growing through the development of portable, miniaturized, lightweight, and highly efficient electronic devices, and demand for lithium secondary batteries capable of realizing large capacity and excellent performance as power sources of these electronic devices is rapidly increasing. Further, as electric vehicles (EVs) and hybrid electric vehicles (HEVs) have been put to practical use, research into lithium secondary batteries having large capacity, excellent output, and high stability has been actively conducted.
A lithium secondary battery is used by injecting an electrolyte solution into a battery cell including a cathode including a cathode active material capable of intercalation and deintercalation of lithium and an anode including an anode active material capable of intercalation and deintercalation of lithium.
Among the components of such a lithium secondary battery, the cathode active material plays an important role in determining the capacity and performance of the battery.
Recently, since energy consumption of mobile devices has been increasing due to the multifunctionality of mobile devices, and further, as the application to the field of environment-friendly electric vehicles has expanded, development of a cathode active material having high energy density has been demanded.
Conventionally, as a method of increasing the energy density of a cathode active material, a method of mixing particles having different sizes in various ratios has been used to increase a volume capacity density, a filling density, or a tapped density of the cathode active material.
For example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2000-082466) discloses a cathode active material in which lithium cobalt composite oxide particles have an average particle diameter in a range of 0.1 micrometers (μm) to 50 μm, and two peaks are found in a particle distribution. According to the above method, the filling density of the cathode active material particles may improve.
Patent Document 2 (Japanese Patent Application Laid-Open No. 2004-119218) discloses mixing a cathode active material having an average particle diameter of 7 μm to 20 μm with a cathode active material having an average particle diameter of 10 percent (%) to 30% of the foregoing cathode active material so as to improve the volume capacity density of the cathode active material.
Patent Document 3 (Korean Patent Application Pub. No. 10-2010-0131921) discloses a cathode active material having an improved filling density by including a small-diameter active material having an average particle diameter of 0.5 μm and a maximum particle diameter of less than 1 μm, and a large-diameter active material having an average particle diameter of 5 μm to 20 μm and a maximum particle diameter of 100 μm.
However, the prior art relies on empirical observations or repetitive experimentation to improve the density of particles by simply mixing particles of various sizes. According to the above methods, the density of a portion of particles may improve limitedly, and it is not possible to recognize as to whether the improved density value is due to the particles itself or due to the particle size distribution of the cathode active material. Thus, it is difficult to recognize the physical property controlling factor.
Accordingly, in the present invention, a size and a volume of interparticular pores are quantified to realize a cathode active material having a high energy density.